Flexible printed wiring boards have been used in various electrical appliances or electronic appliances. For the purpose of realizing size reduction and weight reduction in these electrical and electronic appliances, the wiring patterns on the flexible printed wiring boards have come to be formed at higher densities and the flexible printed wiring boards have come to have miniaturized parts mounted thereon at higher densities.
In general, the wiring pattern on a flexible printed wiring board is formed by laminating a copper foil as a metal foil to an insulating layer, e.g., a polyimide film, with heating by means of a thermosetting adhesive, further elevating the temperature thereof to cure the thermosetting adhesive, and then etching the copper foil (see, for example, patent document 1).
Patent Document 1: JP 2002-326308 A
However, after the selective removal of the copper foil by etching, the actual dimensions of the flexible printed wiring board change considerably from the design dimensions due to the internal stress which has accumulated in the flexible printed wiring board. As a result, there are cases where parts to be mounted are mounted in positions shifted from the design positions, making it impossible to connect the mounted parts to the flexible printed wiring board.